Plant Health Problems
Diseases caused by Fungi:
Powdery mildew, Erysiphe.
White powdery spots or patches develop on leaves and stems. Symptoms often first appear on the upper surfaces of the leaves. Heavily infected leaves turn brown and shrivel.
Disease can be minimized by avoiding overcrowded spacing of plants and by carefully picking off affected leaves as soon as symptoms are evident. Symptomatic leaves can be placed into a plastic bag in order to avoid spreading the spores of the fungus to other plants. Use of fungicides is usually not necessary. However, for ornamental plants, applications can be made as soon as symptoms are visible. Among the compounds registered for use in Connecticut are thiophanate-methyl, potassium bicarbonate, and sulfur. Consult the label for dosage rates and safety precautions.
Aphids, Aphis monardae.
Beebalm is rarely infested by the aphid, Aphis monardae. When needed, it may be managed by spraying with insecticidal soap, ultra-fine horticultural oil or malathion, which are among the compounds registered for control of this pest in Connecticut. Consult the label for dosage rates and safety precautions.
Stalk borer, Papaipema nebris.
The stalk borer occasionally tunnels in beebalm. This borer infests an occasional stalk of many kinds of herbaceous plants and it frequently causes rather severe injury to dahlia. As a rule its presence escapes notice until the plant begins to wilt. Then it is too late for the plant to recover. The larva tunnels up and down inside the stem, and the top portion usually wilts and later dies. There is one annual generation. The moths emerge in September and October and lay eggs on the stalks of their food plants, in which stage the insect passes the winter. The eggs hatch in May or early June. The young larva begins to feed on the leaves of the nearest food plant, and later tunnels in the stem. The mature larva is nearly 1 1/2 inches in length, grayish brown with one white dorsal stripe and two white lateral stripes on each side. On the front half of the body the lateral stripes are interrupted, and the lower brown stripe extends forward onto the side of the head.
Burning all the old stalks (if allowed) and destroying weeds at the edges of the garden helps control this insect. When needed, methoxychlor, which is among the compounds registered for use against this pest in Connecticut, applied as a dust in June, should control this pest. Consult the label for dosage rates and safety precautions.
Thrips, Frankliniella spp.
These small whitish insects feed on pollen and flower petals. The adults may have wings equal or greater than the body length. The four wings are veinless with long hairs on the leading and trailing edge. Thrips pierce plant tissues to feed, damaging them. They quickly scurry into hiding when the plant is touched or they sense changes in the environment. Thrips are readily detected by exhaling on a blossom held over your hand, or tapping the blossom onto a white sheet of paper. The carbon dioxide in the breath will cause the thrips to exit the bloom and fall into your hand. Spinosad is an effective product against flower thrips. Consult the label for dosage rates and safety precautions.
Twospotted spider mite, Tetranychus urticae.
This pest infests the undersides of the leaves, which become light yellow, and the plants have a generally unhealthy appearance. Sometimes the mites form webs, which more or less enclose the upper as well as the lower leaf surface. Among the compounds registered for control of this pest in Connecticut are insecticidal soap and ultrafine horticultural oil. Spraying with insecticidal soap will give sufficient control if applied at least twice at 7-10 day intervals. The predatory mite, Neoseiulus fallacis, is most commonly found feeding where there are mite infestations. A single application of ultrafine horticultural oil (1% dilution) can be effective if predatory mites are present. Special care should be taken with soap or oil to obtain thorough spray coverage, because they only work on contact. Abamectin is an effective restricted use material. Consult the label for dosage rates and safety precautions. Avoid applying carbaryl or pyrethroids, which tend to be much more toxic to the predators than to the pest spider mites.